Roasted coffee beans are known to change flavor as time elapses after roasting. Liquid extract thereof which serves as a drink is also known to largely change flavor over time. Generally, liquid coffee extract quickly changes flavor—“drink within thirty minutes after extraction”—as is said. It is difficult to keep the liquid extract without causing change in flavor.
However, considering the trouble and the costs of extraction, many of the large-scale casual restaurants and fast food restaurants serves coffee brewed in advance and kept in thermal pots until served. Therefore, depending on the frequency of customer orders, the coffee which has changed flavor due to long time holding after extraction at high temperature has to be served to customers. Or, the coffee has to be disposed of when certain time elapses after extraction. As above, long time storage of coffee without degradation of flavor is a critical issue for the food service industry which serves non-instant coffee. Nevertheless, no effective measures have been taken.
Unexamined Japanese Patent Publication Nos. 8-322467, 11-225673, and 2001-112416 disclose techniques for inhibiting change in flavor of non-instant coffee. In these publications, pH adjusters, sugars, antioxidant and/or synthetic preservatives are added to liquid coffee extract. The publications are mainly concerned with coffee beverages in containers such as canned coffee.